Rate matching for coordinated multipoint transmission schemes

ABSTRACT

Certain aspects of the present disclosure relate to techniques for determining resource elements REs used for Coordinated Multipoint (CoMP) transmission schemes. The techniques generally include determining, by a User Equipment (UE), a set of data REs used for Coordinated Multipoint (CoMP) operation. The determination is based on a CoMP scheme and data REs available to particular base stations involved in the CoMP operation. The technique further includes processing data received via the CoMP operation on the determined set of data REs.

CLAIM OF PRIORITY UNDER 35 U.S.C. § 119

The present application for patent claims benefit of U.S. ProvisionalPatent Application Ser. No. 61/433,448, filed Jan. 17, 2011 and assignedto the assignee hereof and hereby expressly incorporated by referenceherein.

BACKGROUND

Field

Certain aspects of the present disclosure generally relate to wirelesscommunications.

Background

Wireless communication systems are widely deployed to provide varioustypes of communication content such as voice, data, and so on. Thesesystems may be multiple-access systems capable of supportingcommunication with multiple users by sharing the available systemresources (e.g., bandwidth and transmit power). Examples of suchmultiple-access systems include Code Division Multiple Access (CDMA)systems, Time Division Multiple Access (TDMA) systems, FrequencyDivision Multiple Access (FDMA) systems, 3^(rd) Generation PartnershipProject (3GPP) Long Term Evolution (LTE) systems, and OrthogonalFrequency Division Multiple Access (OFDMA) systems.

In recent additions to wireless communication systems, under the socalled LTE-Advanced feature set (e.g. 3GPP TS 36.920), differentfunctionalities are defined for which several cells cooperate togetherto increase spectral efficiency, the quality and performance of the airinterface. An example of such a functionality is the CoordinatedMulti-Point (CoMP) that has been introduced to increase system spectralefficiency in a MIMO-like approach and is about to be fully standardizedby the 3^(rd) Generation Partnership Project (3GPP).

SUMMARY

Certain aspects of the present disclosure provide a method for wirelesscommunications by a user equipment. The method generally includesdetermining, by the UE, a set of data resource elements (REs) used forCoordinated Multipoint (CoMP) operation, wherein the determination isbased on a CoMP scheme and data REs available to particular basestations involved in the CoMP operation, and processing data receivedvia the CoMP operation on the determined set of data REs.

Certain aspects of the present disclosure provide a method for wirelesscommunications by a first base station. The method generally includesdetermining a set of data resource elements (REs) used by particularbase stations, including the first base station, for CoordinatedMultipoint (CoMP) operation to a user equipment (UE), and transmittingdata via the CoMP operation on the determined set of data REs to the UE.

Certain aspects of the present disclosure provide an apparatus forwireless communications. The apparatus generally includes means fordetermining, by the apparatus, a set of data resource elements (REs)used for Coordinated Multipoint (CoMP) operation, wherein the means fordetermining determine based on a CoMP scheme and data REs available toparticular base stations involved in the CoMP operation, and means forprocessing data received via the CoMP operation on the determined set ofdata REs.

Certain aspects of the present disclosure provide an apparatus forwireless communications. The apparatus generally includes means fordetermining a set of data resource elements (REs) used by particularbase stations, including a first base station, for CoordinatedMultipoint (CoMP) operation to a user equipment (UE), and means fortransmitting data via the CoMP operation on the determined set of dataREs to the UE.

Certain aspects of the present disclosure provide an apparatus forwireless communications. The apparatus generally includes a processingsystem configured to determine, by the apparatus, a set of data resourceelements (REs) used for Coordinated Multipoint (CoMP) operation, whereinthe determination is based on a CoMP scheme and data REs available toparticular base stations involved in the CoMP operation, and processdata received via the CoMP operation on the determined set of data REs.

Certain aspects of the present disclosure provide an apparatus forwireless communications. The apparatus generally includes a processingsystem and a transmitter. The processing system is configured todetermine a set of data resource elements (REs) used by particular basestations for Coordinated Multipoint (CoMP) operation to a user equipment(UE). The transmitter configured to transmit data via the CoMP operationon the determined set of data REs to the UE.

Certain aspects of the present disclosure provide a computer-programproduct for wireless communications. The computer-program productgenerally includes a computer-readable medium having code fordetermining, by a UE, a set of data resource elements (REs) used forCoordinated Multipoint (CoMP) operation, wherein the determination isbased on a CoMP scheme and data REs available to particular basestations involved in the CoMP operation, and processing data receivedvia the CoMP operation on the determined set of data REs.

Certain aspects of the present disclosure provide a computer-programproduct for wireless communications. The computer-program productgenerally includes a computer-readable medium having code fordetermining a set of data resource elements (REs) used by particularbase stations for Coordinated Multipoint (CoMP) operation to a userequipment (UE), and transmitting data via the CoMP operation on thedetermined set of data REs to the UE.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above-recited features of the presentdisclosure can be understood in detail, a more particular description,briefly summarized above, may be had by reference to aspects, some ofwhich are illustrated in the appended drawings. It is to be noted,however, that the appended drawings illustrate only certain typicalaspects of this disclosure and are therefore not to be consideredlimiting of its scope, for the description may admit to other equallyeffective aspects.

FIG. 1 is a diagram illustrating an example of a network architecture.

FIG. 2 is a diagram illustrating an example of an access network.

FIG. 3 is a diagram illustrating an example of a DL frame structure inLTE.

FIG. 4 is a diagram illustrating an example of an UL frame structure inLTE.

FIG. 5 is a diagram illustrating an example of a radio protocolarchitecture for the user and control planes.

FIG. 6 is a diagram illustrating an example of an evolved Node B anduser equipment in an access network.

FIG. 7 illustrates an example CoMP system.

FIG. 8 illustrates an example determination of data REs for use by basestation in a CoMP system, in accordance with aspects of the presentdisclosure.

FIG. 9 illustrates example operations 900 that may be performed by auser equipment (UE) to process CoMP transmissions, in accordance withcertain aspects of the present disclosure.

FIG. 10 illustrates example operations 1000 that may be performed by abase station to process CoMP transmissions, in accordance with certainaspects of the present disclosure.

DETAILED DESCRIPTION

The detailed description set forth below in connection with the appendeddrawings is intended as a description of various configurations and isnot intended to represent the only configurations in which the conceptsdescribed herein may be practiced. The detailed description includesspecific details for the purpose of providing a thorough understandingof various concepts. However, it will be apparent to those skilled inthe art that these concepts may be practiced without these specificdetails. In some instances, well known structures and components areshown in block diagram form in order to avoid obscuring such concepts.

Several aspects of telecommunication systems will now be presented withreference to various apparatus and methods. These apparatus and methodswill be described in the following detailed description and illustratedin the accompanying drawings by various blocks, modules, components,circuits, steps, processes, algorithms, etc. (collectively referred toas “elements”). These elements may be implemented using electronichardware, computer software, or any combination thereof. Whether suchelements are implemented as hardware or software depends upon theparticular application and design constraints imposed on the overallsystem.

By way of example, an element, or any portion of an element, or anycombination of elements may be implemented with a “processing system”that includes one or more processors. Examples of processors includemicroprocessors, microcontrollers, digital signal processors (DSPs),field programmable gate arrays (FPGAs), programmable logic devices(PLDs), state machines, gated logic, discrete hardware circuits, andother suitable hardware configured to perform the various functionalitydescribed throughout this disclosure. One or more processors in theprocessing system may execute software. Software shall be construedbroadly to mean instructions, instruction sets, code, code segments,program code, programs, subprograms, software modules, applications,software applications, software packages, routines, subroutines,objects, executables, threads of execution, procedures, functions, etc.,whether referred to as software, firmware, middleware, microcode,hardware description language, or otherwise.

Accordingly, in one or more exemplary embodiments, the functionsdescribed may be implemented in hardware, software, firmware, or anycombination thereof. If implemented in software, the functions may bestored on or encoded as one or more instructions or code on acomputer-readable medium. Computer-readable media includes computerstorage media. Storage media may be any available media that can beaccessed by a computer. By way of example, and not limitation, suchcomputer-readable media can comprise RAM, ROM, EEPROM, CD-ROM or otheroptical disk storage, magnetic disk storage or other magnetic storagedevices, or any other medium that can be used to carry or store desiredprogram code in the form of instructions or data structures and that canbe accessed by a computer. Disk and disc, as used herein, includescompact disc (CD), laser disc, optical disc, digital versatile disc(DVD), floppy disk and Blu-ray disc where disks usually reproduce datamagnetically, while discs reproduce data optically with lasers.Combinations of the above should also be included within the scope ofcomputer-readable media.

FIG. 1 is a diagram illustrating a LTE network architecture 100. The LTEnetwork architecture 100 may be referred to as an Evolved Packet System(EPS) 100. The EPS 100 may include one or more user equipment (UE) 102,an Evolved UMTS Terrestrial Radio Access Network (E-UTRAN) 104, anEvolved Packet Core (EPC) 110, a Home Subscriber Server (HSS) 120, andan Operator's IP Services 122. The EPS can interconnect with otheraccess networks, but for simplicity those entities/interfaces are notshown. As shown, the EPS provides packet-switched services, however, asthose skilled in the art will readily appreciate, the various conceptspresented throughout this disclosure may be extended to networksproviding circuit-switched services.

The E-UTRAN includes the evolved Node B (eNB) 106 and other eNBs 108.The eNB 106 provides user and control planes protocol terminationstoward the UE 102. The eNB 106 may be connected to the other eNBs 108via an X2 interface (e.g., backhaul). The eNB 106 may also be referredto as a base station, a base transceiver station, a radio base station,a radio transceiver, a transceiver function, a basic service set (BSS),an extended service set (ESS), or some other suitable terminology. TheeNB 106 provides an access point to the EPC 110 for a UE 102. Examplesof UEs 102 include a cellular phone, a smart phone, a session initiationprotocol (SIP) phone, a laptop, a personal digital assistant (PDA), asatellite radio, a global positioning system, a multimedia device, avideo device, a digital audio player (e.g., MP3 player), a camera, agame console, or any other similar functioning device. The UE 102 mayalso be referred to by those skilled in the art as a mobile station, asubscriber station, a mobile unit, a subscriber unit, a wireless unit, aremote unit, a mobile device, a wireless device, a wirelesscommunications device, a remote device, a mobile subscriber station, anaccess terminal, a mobile terminal, a wireless terminal, a remoteterminal, a handset, a user agent, a mobile client, a client, or someother suitable terminology.

The eNB 106 is connected by an S1 interface to the EPC 110. The EPC 110includes a Mobility Management Entity (MME) 112, other MMEs 114, aServing Gateway 116, and a Packet Data Network (PDN) Gateway 118. TheMME 112 is the control node that processes the signaling between the UE102 and the EPC 110. Generally, the MME 112 provides bearer andconnection management. All user IP packets are transferred through theServing Gateway 116, which itself is connected to the PDN Gateway 118.The PDN Gateway 118 provides UE IP address allocation as well as otherfunctions. The PDN Gateway 118 is connected to the Operator's IPServices 122. The Operator's IP Services 122 may include the Internet,the Intranet, an IP Multimedia Subsystem (IMS), and a PS StreamingService (PSS).

FIG. 2 is a diagram illustrating an example of an access network 200 inan LTE network architecture. In this example, the access network 200 isdivided into a number of cellular regions (cells) 202. One or more lowerpower class eNBs 208 may have cellular regions 210 that overlap with oneor more of the cells 202. A lower power class eNB 208 may be referred toas a remote radio head (RRH). The lower power class eNB 208 may be afemto cell (e.g., home eNB (HeNB)), pico cell, or micro cell. The macroeNBs 204 are each assigned to a respective cell 202 and are configuredto provide an access point to the EPC 110 for all the UEs 206 in thecells 202. There is no centralized controller in this example of anaccess network 200, but a centralized controller may be used inalternative configurations. The eNBs 204 are responsible for all radiorelated functions including radio bearer control, admission control,mobility control, scheduling, security, and connectivity to the servinggateway 116.

The modulation and multiple access scheme employed by the access network200 may vary depending on the particular telecommunications standardbeing deployed. In LTE applications, OFDM is used on the DL and SC-FDMAis used on the UL to support both frequency division duplexing (FDD) andtime division duplexing (TDD). As those skilled in the art will readilyappreciate from the detailed description to follow, the various conceptspresented herein are well suited for LTE applications. However, theseconcepts may be readily extended to other telecommunication standardsemploying other modulation and multiple access techniques. By way ofexample, these concepts may be extended to Evolution-Data Optimized(EV-DO) or Ultra Mobile Broadband (UMB). EV-DO and UMB are air interfacestandards promulgated by the 3rd Generation Partnership Project 2(3GPP2) as part of the CDMA2000 family of standards and employs CDMA toprovide broadband Internet access to mobile stations. These concepts mayalso be extended to Universal Terrestrial Radio Access (UTRA) employingWideband-CDMA (W-CDMA) and other variants of CDMA, such as TD-SCDMA;Global System for Mobile Communications (GSM) employing TDMA; andEvolved UTRA (E-UTRA), IEEE 802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE802.20, and Flash-OFDM employing OFDMA. UTRA, E-UTRA, UMTS, LTE and GSMare described in documents from the 3GPP organization. CDMA2000 and UMBare described in documents from the 3GPP2 organization. The actualwireless communication standard and the multiple access technologyemployed will depend on the specific application and the overall designconstraints imposed on the system.

The eNBs 204 may have multiple antennas supporting MIMO technology. Theuse of MIMO technology enables the eNBs 204 to exploit the spatialdomain to support spatial multiplexing, beamforming, and transmitdiversity. Spatial multiplexing may be used to transmit differentstreams of data simultaneously on the same frequency. The data steamsmay be transmitted to a single UE 206 to increase the data rate or tomultiple UEs 206 to increase the overall system capacity. This isachieved by spatially precoding each data stream (i.e., applying ascaling of an amplitude and a phase) and then transmitting eachspatially precoded stream through multiple transmit antennas on the DL.The spatially precoded data streams arrive at the UE(s) 206 withdifferent spatial signatures, which enables each of the UE(s) 206 torecover the one or more data streams destined for that UE 206. On theUL, each UE 206 transmits a spatially precoded data stream, whichenables the eNB 204 to identify the source of each spatially precodeddata stream.

Spatial multiplexing is generally used when channel conditions are good.When channel conditions are less favorable, beamforming may be used tofocus the transmission energy in one or more directions. This may beachieved by spatially precoding the data for transmission throughmultiple antennas. To achieve good coverage at the edges of the cell, asingle stream beamforming transmission may be used in combination withtransmit diversity.

In the detailed description that follows, various aspects of an accessnetwork will be described with reference to a MIMO system supportingOFDM on the DL. OFDM is a spread-spectrum technique that modulates dataover a number of subcarriers within an OFDM symbol. The subcarriers arespaced apart at precise frequencies. The spacing provides“orthogonality” that enables a receiver to recover the data from thesubcarriers. In the time domain, a guard interval (e.g., cyclic prefix)may be added to each OFDM symbol to combat inter-OFDM-symbolinterference. The UL may use SC-FDMA in the form of a DFT-spread OFDMsignal to compensate for high peak-to-average power ratio (PAPR).

FIG. 3 is a diagram 300 illustrating an example of a DL frame structurein LTE. A frame (10 ms) may be divided into 10 equally sized sub-frames.Each sub-frame may include two consecutive time slots. A resource gridmay be used to represent two time slots, each time slot including aresource block. The resource grid is divided into multiple resourceelements. In LTE, a resource block contains 12 consecutive subcarriersin the frequency domain and, for a normal cyclic prefix in each OFDMsymbol, 7 consecutive OFDM symbols in the time domain, or 84 resourceelements. For an extended cyclic prefix, a resource block contains 6consecutive OFDM symbols in the time domain and has 72 resourceelements. Some of the resource elements, as indicated as R 302, 304,include DL reference signals (DL-RS). The DL-RS include Cell-specific RS(CRS) (also sometimes called common RS) 302 and UE-specific RS (UE-RS)304. UE-RS 304 are transmitted only on the resource blocks upon whichthe corresponding physical DL shared channel (PDSCH) is mapped. Thenumber of bits carried by each resource element depends on themodulation scheme. Thus, the more resource blocks that a UE receives andthe higher the modulation scheme, the higher the data rate for the UE.

FIG. 4 is a diagram 400 illustrating an example of an UL frame structurein LTE. The available resource blocks for the UL may be partitioned intoa data section and a control section. The control section may be formedat the two edges of the system bandwidth and may have a configurablesize. The resource blocks in the control section may be assigned to UEsfor transmission of control information. The data section may includeall resource blocks not included in the control section. The UL framestructure results in the data section including contiguous subcarriers,which may allow a single UE to be assigned all of the contiguoussubcarriers in the data section.

A UE may be assigned resource blocks 410 a, 410 b in the control sectionto transmit control information to an eNB. The UE may also be assignedresource blocks 420 a, 420 b in the data section to transmit data to theeNB. The UE may transmit control information in a physical UL controlchannel (PUCCH) on the assigned resource blocks in the control section.The UE may transmit only data or both data and control information in aphysical UL shared channel (PUSCH) on the assigned resource blocks inthe data section. A UL transmission may span both slots of a subframeand may hop across frequency.

A set of resource blocks may be used to perform initial system accessand achieve UL synchronization in a physical random access channel(PRACH) 430. The PRACH 430 carries a random sequence and cannot carryany UL data/signaling. Each random access preamble occupies a bandwidthcorresponding to six consecutive resource blocks. The starting frequencyis specified by the network. That is, the transmission of the randomaccess preamble is restricted to certain time and frequency resources.There is no frequency hopping for the PRACH. The PRACH attempt iscarried in a single subframe (1 ms) or in a sequence of few contiguoussubframes and a UE can make only a single PRACH attempt per frame (10ms).

FIG. 5 is a diagram 500 illustrating an example of a radio protocolarchitecture for the user and control planes in LTE. The radio protocolarchitecture for the UE and the eNB is shown with three layers: Layer 1,Layer 2, and Layer 3. Layer 1 (L1 layer) is the lowest layer andimplements various physical layer signal processing functions. The L1layer will be referred to herein as the physical layer 506. Layer 2 (L2layer) 508 is above the physical layer 506 and is responsible for thelink between the UE and eNB over the physical layer 506.

In the user plane, the L2 layer 508 includes a media access control(MAC) sublayer 510, a radio link control (RLC) sublayer 512, and apacket data convergence protocol (PDCP) 514 sublayer, which areterminated at the eNB on the network side. Although not shown, the UEmay have several upper layers above the L2 layer 508 including a networklayer (e.g., IP layer) that is terminated at the PDN gateway 118 on thenetwork side, and an application layer that is terminated at the otherend of the connection (e.g., far end UE, server, etc.).

The PDCP sublayer 514 provides multiplexing between different radiobearers and logical channels. The PDCP sublayer 514 also provides headercompression for upper layer data packets to reduce radio transmissionoverhead, security by ciphering the data packets, and handover supportfor UEs between eNBs. The RLC sublayer 512 provides segmentation andreassembly of upper layer data packets, retransmission of lost datapackets, and reordering of data packets to compensate for out-of-orderreception due to hybrid automatic repeat request (HARQ). The MACsublayer 510 provides multiplexing between logical and transportchannels. The MAC sublayer 510 is also responsible for allocating thevarious radio resources (e.g., resource blocks) in one cell among theUEs. The MAC sublayer 510 is also responsible for HARQ operations.

In the control plane, the radio protocol architecture for the UE and eNBis substantially the same for the physical layer 506 and the L2 layer508 with the exception that there is no header compression function forthe control plane. The control plane also includes a radio resourcecontrol (RRC) sublayer 516 in Layer 3 (L3 layer). The RRC sublayer 516is responsible for obtaining radio resources (i.e., radio bearers) andfor configuring the lower layers using RRC signaling between the eNB andthe UE.

FIG. 3 is a diagram 300 illustrating an example of a DL frame structurein LTE. A frame (10 ms) may be divided into 10 equally sized sub-frames.Each sub-frame may include two consecutive time slots. A resource gridmay be used to represent two time slots, each time slot including aresource block. The resource grid is divided into multiple resourceelements. In LTE, a resource block contains 12 consecutive subcarriersin the frequency domain and, for a normal cyclic prefix in each OFDMsymbol, 7 consecutive OFDM symbols in the time domain, or 84 resourceelements. For an extended cyclic prefix, a resource block contains 6consecutive OFDM symbols in the time domain and has 72 resourceelements. Some of the resource elements, as indicated as R 302, 304,include DL reference signals (DL-RS). The DL-RS include Cell-specific RS(CRS) (also sometimes called common RS) 302 and UE-specific RS (UE-RS)304. UE-RS 304 are transmitted only on the resource blocks upon whichthe corresponding physical DL shared channel (PDSCH) is mapped. Thenumber of bits carried by each resource element depends on themodulation scheme. Thus, the more resource blocks that a UE receives andthe higher the modulation scheme, the higher the data rate for the UE.

FIG. 4 is a diagram 400 illustrating an example of an UL frame structurein LTE. The available resource blocks for the UL may be partitioned intoa data section and a control section. The control section may be formedat the two edges of the system bandwidth and may have a configurablesize. The resource blocks in the control section may be assigned to UEsfor transmission of control information. The data section may includeall resource blocks not included in the control section. The UL framestructure results in the data section including contiguous subcarriers,which may allow a single UE to be assigned all of the contiguoussubcarriers in the data section.

A UE may be assigned resource blocks 410 a, 410 b in the control sectionto transmit control information to an eNB. The UE may also be assignedresource blocks 420 a, 420 b in the data section to transmit data to theeNB. The UE may transmit control information in a physical UL controlchannel (PUCCH) on the assigned resource blocks in the control section.The UE may transmit only data or both data and control information in aphysical UL shared channel (PUSCH) on the assigned resource blocks inthe data section. A UL transmission may span both slots of a subframeand may hop across frequency.

A set of resource blocks may be used to perform initial system accessand achieve UL synchronization in a physical random access channel(PRACH) 430. The PRACH 430 carries a random sequence and cannot carryany UL data/signaling. Each random access preamble occupies a bandwidthcorresponding to six consecutive resource blocks. The starting frequencyis specified by the network. That is, the transmission of the randomaccess preamble is restricted to certain time and frequency resources.There is no frequency hopping for the PRACH. The PRACH attempt iscarried in a single subframe (1 ms) or in a sequence of few contiguoussubframes and a UE can make only a single PRACH attempt per frame (10ms).

FIG. 5 is a diagram 500 illustrating an example of a radio protocolarchitecture for the user and control planes in LTE. The radio protocolarchitecture for the UE and the eNB is shown with three layers: Layer 1,Layer 2, and Layer 3. Layer 1 (L1 layer) is the lowest layer andimplements various physical layer signal processing functions. The L1layer will be referred to herein as the physical layer 506. Layer 2 (L2layer) 508 is above the physical layer 506 and is responsible for thelink between the UE and eNB over the physical layer 506.

In the user plane, the L2 layer 508 includes a media access control(MAC) sublayer 510, a radio link control (RLC) sublayer 512, and apacket data convergence protocol (PDCP) 514 sublayer, which areterminated at the eNB on the network side. Although not shown, the UEmay have several upper layers above the L2 layer 508 including a networklayer (e.g., IP layer) that is terminated at the PDN gateway 118 on thenetwork side, and an application layer that is terminated at the otherend of the connection (e.g., far end UE, server, etc.).

The PDCP sublayer 514 provides multiplexing between different radiobearers and logical channels. The PDCP sublayer 514 also provides headercompression for upper layer data packets to reduce radio transmissionoverhead, security by ciphering the data packets, and handover supportfor UEs between eNBs. The RLC sublayer 512 provides segmentation andreassembly of upper layer data packets, retransmission of lost datapackets, and reordering of data packets to compensate for out-of-orderreception due to hybrid automatic repeat request (HARQ). The MACsublayer 510 provides multiplexing between logical and transportchannels. The MAC sublayer 510 is also responsible for allocating thevarious radio resources (e.g., resource blocks) in one cell among theUEs. The MAC sublayer 510 is also responsible for HARQ operations.

In the control plane, the radio protocol architecture for the UE and eNBis substantially the same for the physical layer 506 and the L2 layer508 with the exception that there is no header compression function forthe control plane. The control plane also includes a radio resourcecontrol (RRC) sublayer 516 in Layer 3 (L3 layer). The RRC sublayer 516is responsible for obtaining radio resources (i.e., radio bearers) andfor configuring the lower layers using RRC signaling between the eNB andthe UE.

FIG. 6 is a block diagram of an eNB 610 in communication with a UE 650in an access network. In the DL, upper layer packets from the corenetwork are provided to a controller/processor 675. Thecontroller/processor 675 implements the functionality of the L2 layer.In the DL, the controller/processor 675 provides header compression,ciphering, packet segmentation and reordering, multiplexing betweenlogical and transport channels, and radio resource allocations to the UE650 based on various priority metrics. The controller/processor 675 isalso responsible for HARQ operations, retransmission of lost packets,and signaling to the UE 650.

The transmit (TX) processor 616 implements various signal processingfunctions for the L1 layer (i.e., physical layer). The signal processingfunctions includes coding and interleaving to facilitate forward errorcorrection (FEC) at the UE 650 and mapping to signal constellationsbased on various modulation schemes (e.g., binary phase-shift keying(BPSK), quadrature phase-shift keying (QPSK), M-phase-shift keying(M-PSK), M-quadrature amplitude modulation (M-QAM)). The coded andmodulated symbols are then split into parallel streams. Each stream isthen mapped to an OFDM subcarrier, multiplexed with a reference signal(e.g., pilot) in the time and/or frequency domain, and then combinedtogether using an Inverse Fast Fourier Transform (IFFT) to produce aphysical channel carrying a time domain OFDM symbol stream. The OFDMstream is spatially precoded to produce multiple spatial streams.Channel estimates from a channel estimator 674 may be used to determinethe coding and modulation scheme, as well as for spatial processing. Thechannel estimate may be derived from a reference signal and/or channelcondition feedback transmitted by the UE 650. Each spatial stream isthen provided to a different antenna 620 via a separate transmitter618TX. Each transmitter 618TX modulates an RF carrier with a respectivespatial stream for transmission.

At the UE 650, each receiver 654RX receives a signal through itsrespective antenna 652. Each receiver 654RX recovers informationmodulated onto an RF carrier and provides the information to the receive(RX) processor 656. The RX processor 656 implements various signalprocessing functions of the L1 layer. The RX processor 656 performsspatial processing on the information to recover any spatial streamsdestined for the UE 650. If multiple spatial streams are destined forthe UE 650, they may be combined by the RX processor 656 into a singleOFDM symbol stream. The RX processor 656 then converts the OFDM symbolstream from the time-domain to the frequency domain using a Fast FourierTransform (FFT). The frequency domain signal comprises a separate OFDMsymbol stream for each subcarrier of the OFDM signal. The symbols oneach subcarrier, and the reference signal, is recovered and demodulatedby determining the most likely signal constellation points transmittedby the eNB 610. These soft decisions may be based on channel estimatescomputed by the channel estimator 658. The soft decisions are thendecoded and deinterleaved to recover the data and control signals thatwere originally transmitted by the eNB 610 on the physical channel. Thedata and control signals are then provided to the controller/processor659.

The controller/processor 659 implements the L2 layer. Thecontroller/processor can be associated with a memory 660 that storesprogram codes and data. The memory 660 may be referred to as acomputer-readable medium. In the UL, the control/processor 659 providesdemultiplexing between transport and logical channels, packetreassembly, deciphering, header decompression, control signal processingto recover upper layer packets from the core network. The upper layerpackets are then provided to a data sink 662, which represents all theprotocol layers above the L2 layer. Various control signals may also beprovided to the data sink 662 for L3 processing. Thecontroller/processor 659 is also responsible for error detection usingan acknowledgement (ACK) and/or negative acknowledgement (NACK) protocolto support HARQ operations.

In the UL, a data source 667 is used to provide upper layer packets tothe controller/processor 659. The data source 667 represents allprotocol layers above the L2 layer. Similar to the functionalitydescribed in connection with the DL transmission by the eNB 610, thecontroller/processor 659 implements the L2 layer for the user plane andthe control plane by providing header compression, ciphering, packetsegmentation and reordering, and multiplexing between logical andtransport channels based on radio resource allocations by the eNB 610.The controller/processor 659 is also responsible for HARQ operations,retransmission of lost packets, and signaling to the eNB 610.

Channel estimates derived by a channel estimator 658 from a referencesignal or feedback transmitted by the eNB 610 may be used by the TXprocessor 668 to select the appropriate coding and modulation schemes,and to facilitate spatial processing. The spatial streams generated bythe TX processor 668 are provided to different antenna 652 via separatetransmitters 654TX. Each transmitter 654TX modulates an RF carrier witha respective spatial stream for transmission.

The UL transmission is processed at the eNB 610 in a manner similar tothat described in connection with the receiver function at the UE 650.Each receiver 618RX receives a signal through its respective antenna620. Each receiver 618RX recovers information modulated onto an RFcarrier and provides the information to a RX processor 670. The RXprocessor 670 may implement the L1 layer.

The controller/processor 675 implements the L2 layer. Thecontroller/processor 675 can be associated with a memory 676 that storesprogram codes and data. The memory 676 may be referred to as acomputer-readable medium. In the UL, the control/processor 675 providesdemultiplexing between transport and logical channels, packetreassembly, deciphering, header decompression, control signal processingto recover upper layer packets from the UE 650. Upper layer packets fromthe controller/processor 675 may be provided to the core network. Thecontroller/processor 675 is also responsible for error detection usingan ACK and/or NACK protocol to support HARQ operations.

Rate Matching for Coordinated Multipoint Transmission Schemes

As noted above, in recent additions to wireless communication systems,such as the so called LTE-Advanced feature set (e.g. 3GPP TS 36.920),different functionalities are defined for which several cells cooperatetogether to increase spectral efficiency, the quality and performance ofthe air interface. An example of such a functionality is CoordinatedMulti-Point (CoMP) operation that has been introduced to increase systemspectral efficiency in a MIMO-like approach (where different basestations involved in a CoMP operation may be considered analogous to aseparate MIMO Tx antenna) and is about to be fully standardized by the3^(rd) Generation Partnership Project (3GPP).

FIG. 7 illustrates an example system, in which a plurality of basestations 710 (e.g., a serving eNB 710 a and a remote radio head RRH 710b) may coordinate transmissions to one or more UEs 720 using one or moreCoMP schemes. Base stations 710 and UEs 720 may be configured toparticipate in CoMP schemes, taking advantage of techniques, describedin greater detail below, to account for different base stationsutilizing different data REs (different numbers and/or locations of dataREs).

As used herein, the term CoMP scheme generally refers to a particularscheme used by multiple base stations to coordinate transmissions to oneor more UEs. Some examples of CoMP schemes include joint transmission,Distributed MIMO, coordinated beamforming, dynamic point switching, andthe like.

In a joint transmission CoMP scheme, multiple base stations (or eNBs)typically transmit the same data meant for a UE. For example, thecoordinating base stations may utilize a joint precoding vector thatspans all of the antennas of all the involved base stations.

In a Distributed MIMO CoMP scheme, multiple base stations typicallytransmit different pieces of data meant for a UE as different MIMOlayers. For example, one layer may be sent by one base station, a secondlayer sent by a second base station, and so on, up to the number ofsupported layers.

In a Coordinated beamforming CoMP scheme, each particular base stationtransmits to its UE (that it serves) using beams that are chosen toreduce interference to UEs served by participating CoMP base stations inother neighboring cells.

In a dynamic point switching CoMP scheme, the serving base station for aUE may change over time within a set of base stations.

One issue with CoMP schemes arises because the particular REs used fordata by the different CoMP base stations are different. The exact numberand location of data REs used by different base stations may bedifferent for one or more various reasons. For example, different basestations may have different numbers of control symbols, leavingdifferent numbers of REs available for data. As other examples, thelocation of CRS may be different, their CSI-RS patterns may bedifferent, and/or their patterns of muted REs may be different. As usedherein, the term muted RE generally refers to REs on which a basestation limits transmission, for example, to reduce interference withother base stations or to facilitate interference measurement for otherbase stations As an example of such limited transmission, some REs maybe transmitted with zero power.

The failure of scheduling and mapping algorithms of CoMP base stationsto take into account the fact that different base stations may transmiton different data REs may result in different modulation symbols beingtransmitted on the same REs. The resulting conflict may lead to reducedperformance, with potentially significant offset to the intended gainsachievable by using CoMP.

One approach to account for different data REs used by different CoMPbase stations is to use CoMP schemes on only a limited type of subframesin which the issues discussed above are mitigated. For example, CoMPschemes may be limited to MBSFN subframes where CRS are not present inthe data region. Unfortunately, differences in muting and CSI-RSpatterns may still cause a mismatch in the location of available dataREs even on MBSFN subframes.

Certain aspects of the present disclosure, however, provide techniquesthat may help address issues created with different available data REsacross different eNBs, across various subframe types.

According to certain aspects, CoMP participating base stations mayensure that modulation symbols transmitted on data REs that are used byall of the participating base stations are the same. UEs involved in theCoMP operation may determine which data REs are used by allparticipating base stations and process the modulation symbolstransmitted thereon, with some assurance there is no conflict.

According to certain aspects, only REs that are data REs across all eNBsinvolved in the CoMP operation may be used. This approach may beparticularly suitable for Joint transmission (with each eNB transmittingthe same symbols on the same common data REs).

According to certain aspects, the determination of REs available fordata transmission in the CoMP operation is based on signaling thatprovides a starting symbol index of data REs. In such cases, the UE maybe signaled, via a semi-static configuration or via a dynamic indicationusing a physical downlink control channel (PDCCH), the starting symbolfor the data channel.

In LTE, up to three symbols can be used for control for large systembandwidths. The number of control symbols can be differently managed ineach of the base stations involved in the CoMP operation. The number ofcontrol symbols for a base station may also change on a per subframebasis. A UE can typically rely on decoding of a physical formatindication channel (PCFICH), possibly combining with a physical H-ARQindicator channel (PHICH), to determine the number of control symbolsused by a cell in a subframe. The starting symbol of data channels istypically the one right after the control region.

A UE with two or more base stations involved in the CoMP operation canbe explicitly indicated a starting symbol index for data transmissionswithout the need to decode PCFICH and/or PHICH from two or more basestations. The starting symbol index can be separately indicated for eachof the particular base stations involved in the CoMP operation. Thisprovides flexibility and efficiency in the CoMP operation. A UE can beexplicitly or implicitly signaled to use one of the starting symbolindices for data reception in a subframe corresponding to a particularbase station for the CoMP operation. As an example, the particular basestation can be linked to the base station in which the PDCCH istransmitted. Alternatively, a single starting symbol index may beindicated for all of the particular base stations involved in the CoMPoperation.

According to certain aspects, the determination of data REs for the CoMPoperation is based on the available data REs for a cell in which thecorresponding physical downlink control channel (PDCCH) is transmitted.The available data REs for the cell carrying the PDCCH can be determinedby the UE the same way as when the UE is not configured with the CoMPoperation. As an example, the UE can decode PCFICH and/or PHICH tofigure out the control region and hence the starting symbol index of thedata region. In addition, based on information of the RS configuration(CRS, CSI-RS, and UE-RS), and possibly other channels (e.g., primarybroadcast channel, primary synchronization channel, secondarysynchronization channel, etc), the UE can determine the set of REsavailable for data transmissions.

According to certain aspects, each eNB may use its data REs. Thisapproach may be suitable for coordinated BF, distributed MIMO, dynamicpoint switching, etc., where there is only a single eNB transmitting tothe UE at a time. However, this approach may present challenges withregard to Joint Transmissions. For example, if such a scheme is used forjoint transmission, the base stations may need to ensure that themodulation symbols they transmit on data REs that are also data REs forother eNBs are the same.

For example, multiple base stations may rate match assuming a subset ofcommon data REs (e.g., a union or intersection) of the data REs andpunctured data locations not available to them. For example, in case ofpunctured data locations, a base station may transmit different symbolson REs corresponding to punctured data location than those transmittedfrom the other base stations. For example, FIG. 8 illustrates an exampleof two base stations (for Cell 1 and Cell 2) with data REs {D,D,D,N} and{D,N,D,D} meaning the fourth location corresponds to an RE for puncturedata for Cell 1 and the second location corresponds to an RE forpuncture data for Cell 2. The base stations may identify modulationsymbols {X1,X2,X3,X4} to transmit with the 1st base stationstransmitting {X1,X2,X3,0} and the 2nd base station transmitting{X1,0,X3,X4}. For demodulating such a scheme, independent channelestimates may be needed from the different eNBs, which may be done, ifneeded, with different UE-RS layers.

FIG. 9 illustrates example operations 900 that may be performed by a UEto process CoMP transmissions, in accordance with certain aspects of thepresent disclosure. The operations may be performed, for example, by theUE 720 shown in FIG. 7 (e.g., utilizing corresponding processors andcomponents shown in FIG. 6).

The operations 900 begin, at 902, by determining, by the UE, a set ofdata resource elements (REs) used for Coordinated Multipoint (CoMP)operation, wherein the determination is based on a CoMP scheme and dataREs available to particular base stations involved in the CoMPoperation. At 904, the UE processes data received via the CoMP operationon the determined set of data REs.

FIG. 10 illustrates example operations 1000 that may be performed by abase station to process CoMP transmissions, in accordance with certainaspects of the present disclosure. The operations may be performed, forexample, by one of the base stations 710 shown in FIG. 7 (e.g.,utilizing corresponding processors and components shown in FIG. 6).

The operations 1000 begin, at 1002, by determining a set of dataresource elements (REs) used by particular base stations, including thebase station, for Coordinated Multipoint (CoMP) operation to a userequipment (UE). At 1004, the first station transmits data via the CoMPoperation on the determined set of data REs to the UE.

In some cases, different solutions for determining data REs may bepicked for different CoMP schemes. According to certain aspects, a UEmay figure out which REs are data REs based on the particular CoMPscheme and the particular base stations involved in the CoMP operation.Such knowledge may be signaled, for example, through semi-staticconfiguration or dynamic indication. For semi-static configuration,higher layer signaling may indicate the involved nodes and relevant CoMPscheme to a UE. For dynamic indication, such knowledge may be conveyedin a PDCCH.

For such a solution to work effectively, a UE involved in the CoMPoperation may need to be aware of at least one of muting configurationand CSI-RS configuration (periodicity, subframe offset, intra subframelocation) of neighboring cells involved in the CoMP operation inaddition to its own. The CSI-RS configuration may, for example, indicateREs used for transmitting CSI-RS by the base stations involved in theCoMP operation. For example, the muting configuration may indicate REsin which the base station(s) involved in the CoMP operation limittransmission.

In certain cases, CSI-RS and/or muting may be dropped on certainsubframes due to collisions with paging. In this case, data REs thatwere previously allocated for CSI-RS/muting may become available fordata transmission. Various approaches may be taken to address thisscenario. As an example, a first approach may simply not treat such REsas data REs. In a second approach, however, a UE may treat these REs asavailable data REs for that particular base station. In this case, forthese data REs to be treated as available data REs, UEs and eNBsaffected by it may have to be made to become aware of (e.g., bydetecting) when the CSI-RS/muting is dropped (e.g., through signaling).

The techniques presented herein may allow for efficient use of data REsin CoMP operations. The techniques presented herein may be applied inCoMP networks utilizing base stations of the same power class(homogenous networks) or CoMP networks utilizing base stations ofdifferent power classes (e.g., heterogeneous networks), as well asnetworks utilizing Relays and remote radio heads (RRHs).

The various operations of methods described above may be performed byany suitable means capable of performing the corresponding functions.The means may include various hardware and/or software component(s)and/or module(s), including, but not limited to a circuit, anapplication specific integrated circuit (ASIC), or processor. Generally,where there are operations illustrated in Figures, those operations mayhave corresponding counterpart means-plus-function components capable ofperforming such operations.

The various illustrative logical blocks, modules and circuits describedin connection with the present disclosure may be implemented orperformed with a general purpose processor, a digital signal processor(DSP), an application specific integrated circuit (ASIC), a fieldprogrammable gate array signal (FPGA) or other programmable logic device(PLD), discrete gate or transistor logic, discrete hardware componentsor any combination thereof designed to perform the functions describedherein. A general-purpose processor may be a microprocessor, but in thealternative, the processor may be any commercially available processor,controller, microcontroller or state machine. A processor may also beimplemented as a combination of computing devices, e.g., a combinationof a DSP and a microprocessor, a plurality of microprocessors, one ormore microprocessors in conjunction with a DSP core, or any other suchconfiguration.

The steps of a method or algorithm described in connection with thepresent disclosure may be embodied directly in hardware, in a softwaremodule executed by a processor, or in a combination of the two. Asoftware module may reside in any form of storage medium that is knownin the art. Some examples of storage media that may be used includerandom access memory (RAM), read only memory (ROM), flash memory, EPROMmemory, EEPROM memory, registers, a hard disk, a removable disk, aCD-ROM and so forth. A software module may comprise a singleinstruction, or many instructions, and may be distributed over severaldifferent code segments, among different programs, and across multiplestorage media. A storage medium may be coupled to a processor such thatthe processor can read information from, and write information to, thestorage medium. In the alternative, the storage medium may be integralto the processor.

The methods disclosed herein comprise one or more steps or actions forachieving the described method. The method steps and/or actions may beinterchanged with one another without departing from the scope of theclaims. In other words, unless a specific order of steps or actions isspecified, the order and/or use of specific steps and/or actions may bemodified without departing from the scope of the claims.

The functions described may be implemented in hardware, software,firmware or any combination thereof. If implemented in software, thefunctions may be stored as one or more instructions on acomputer-readable medium. A storage media may be any available mediathat can be accessed by a computer. By way of example, and notlimitation, such computer-readable media can comprise RAM, ROM, EEPROM,CD-ROM or other optical disk storage, magnetic disk storage or othermagnetic storage devices, or any other medium that can be used to carryor store desired program code in the form of instructions or datastructures and that can be accessed by a computer. Disk and disc, asused herein, include compact disc (CD), laser disc, optical disc,digital versatile disc (DVD), floppy disk and Blu-ray® disc where disksusually reproduce data magnetically, while discs reproduce dataoptically with lasers.

Thus, certain aspects may comprise a computer program product forperforming the operations presented herein. For example, such a computerprogram product may comprise a computer readable medium havinginstructions stored (and/or encoded) thereon, the instructions beingexecutable by one or more processors to perform the operations describedherein. For certain aspects, the computer program product may includepackaging material.

Software or instructions may also be transmitted over a transmissionmedium. For example, if the software is transmitted from a website,server, or other remote source using a coaxial cable, fiber optic cable,twisted pair, digital subscriber line (DSL), or wireless technologiessuch as infrared, radio, and microwave, then the coaxial cable, fiberoptic cable, twisted pair, DSL, or wireless technologies such asinfrared, radio, and microwave are included in the definition oftransmission medium.

Further, it should be appreciated that modules and/or other appropriatemeans for performing the methods and techniques described herein can bedownloaded and/or otherwise obtained by a user terminal and/or basestation as applicable. For example, such a device can be coupled to aserver to facilitate the transfer of means for performing the methodsdescribed herein. Alternatively, various methods described herein can beprovided via storage means (e.g., RAM, ROM, a physical storage mediumsuch as a compact disc (CD) or floppy disk, etc.), such that a userterminal and/or base station can obtain the various methods uponcoupling or providing the storage means to the device. Moreover, anyother suitable technique for providing the methods and techniquesdescribed herein to a device can be utilized.

It is to be understood that the claims are not limited to the preciseconfiguration and components illustrated above. Various modifications,changes and variations may be made in the arrangement, operation anddetails of the methods and apparatus described above without departingfrom the scope of the claims.

While the foregoing is directed to aspects of the present disclosure,other and further aspects of the disclosure may be devised withoutdeparting from the basic scope thereof, and the scope thereof isdetermined by the claims that follow.

What is claimed is:
 1. A method for wireless communications by a userequipment (UE), comprising: determining, by the UE, a set of dataresource elements (REs) used for a Coordinated Multipoint (CoMP)operation, wherein the determination is based on data REs available tothe CoMP operation and signaling that provides a starting symbol indexof data REs; and processing, by the UE, data received via the CoMPoperation on the determined set of data REs, wherein processing the datareceived via the CoMP operation comprises processing common modulationsymbols transmitted by each of a plurality of base stations involved inthe CoMP operation on a subset of the determined set of data REs.
 2. Themethod of claim 1, wherein the determination is further based on anintersection of data REs used by each of the base stations involved inthe CoMP operation.
 3. The method of claim 1, wherein the signaling thatprovides the starting symbol index of data REs is provided via asemi-static configuration.
 4. The method of claim 1, wherein thesignaling that provides the starting symbol index of data REs isprovided via a dynamic indication conveyed using a physical downlinkcontrol channel (PDCCH).
 5. The method of claim 1, wherein the startingsymbol index is separately indicated for each of the base stationsinvolved in the CoMP operation.
 6. The method of claim 1, wherein asingle starting symbol index is indicated for all of the base stationsinvolved in the CoMP operation.
 7. The method of claim 1, wherein thedetermination is further based on the available data REs for a cell inwhich a physical downlink control channel (PDCCH) is transmitted.
 8. Themethod of claim 1, wherein the determination is further based on a unionof data REs used by each of the base stations involved in the CoMPoperation.
 9. The method of claim 1, wherein: the determination isfurther based on REs corresponding to data locations not available tothe CoMP operation; and processing the data received via the CoMPoperation further comprises processing different modulation symbols thanthe common modulation symbols from the base stations on REscorresponding to the data locations not available to the CoMP operation.10. The method of claim 1, wherein the determination is further based onat least one of: a channel state information reference signal (CSI-RS)configuration indicating REs used for transmitting CSI-RS by the basestations involved in the CoMP operation; and a muting configurationindicating REs in which the base stations involved in the CoMP operationlimit transmission.
 11. The method of claim 10, further comprising:detecting, by the UE, that at least one of CSI-RS and muting is droppedon certain subframes; and wherein the determination comprisesdetermining that one or more data REs previously allocated for at leastone of CSI-RS or muting become available for data transmission on thosecertain subframes.
 12. The method of claim 1, further comprisingreceiving, by the UE, signaling that provides an indication of a type ofCoMP scheme used for the CoMP operation, wherein the signaling thatprovides the indication of the type of CoMP scheme used for the CoMPoperation is provided via a semi-static configuration.
 13. The method ofclaim 1, further comprising receiving, by the UE, signaling thatprovides an indication of a type of CoMP scheme used for the CoMPoperation, wherein the signaling that provides the indication of thetype of CoMP scheme used for the CoMP operation is provided via adynamic indication conveyed using a physical downlink control channel(PDCCH).
 14. The method of claim 1, wherein the base stations involvedin the CoMP operation comprise base stations of different power classesin a heterogeneous network.
 15. The method of claim 1, wherein the datais received from each of the base stations involved in the CoMPoperation.
 16. The method of claim 1, wherein the data is received froma subset of the base stations involved in the CoMP operation.
 17. Anapparatus for wireless communications, comprising: means fordetermining, by the apparatus, a set of data resource elements (REs)used for a Coordinated Multipoint (CoMP) operation, wherein the meansfor determining determine based on data REs available to the CoMPoperation and signaling that provides a starting symbol index of dataREs; and means for processing, by the apparatus, data received via theCoMP operation on the determined set of data REs, wherein means forprocessing the data received via the CoMP operation comprises means forprocessing common modulation symbols transmitted by each of a pluralityof base stations involved in the CoMP operation on a subset of thedetermined set of data REs.
 18. The apparatus of claim 17, wherein themeans for determining further determine based on an intersection of dataREs used by each of the base stations involved in the CoMP operation.19. The apparatus of claim 17, wherein the signaling that provides thestarting symbol index of data REs is provided via a semi-staticconfiguration.
 20. The apparatus of claim 17, wherein the signaling thatprovides the starting symbol index of data REs is provided via a dynamicindication conveyed using a physical downlink control channel (PDCCH).21. The apparatus of claim 17, wherein the starting symbol index isseparately indicated for each of the base stations involved in the CoMPoperation.
 22. The apparatus of claim 17, wherein a single startingsymbol index is indicated for all of the base stations involved in theCoMP operation.
 23. The apparatus of claim 17, wherein the means fordetermining further determine based on the available data REs for a cellin which a physical downlink control channel (PDCCH) is transmitted. 24.The apparatus of claim 17, wherein the means for determining furtherdetermine based on a union of data REs used by each of the base stationsinvolved in the CoMP operation.
 25. The apparatus of claim 17, wherein:the means for determining further determine based on REs correspondingto data locations not available to the CoMP operation; and the means forprocessing the data received via the CoMP operation further comprisesmeans for processing different modulation symbols than the commonmodulation symbols from the base stations on REs corresponding to thedata locations not available to the CoMP operation.
 26. The apparatus ofclaim 17, wherein the means for determining further determine based onat least one of: a channel state information reference signal (CSI-RS)configuration indicating REs used for transmitting CSI-RS by the basestations involved in the CoMP operation; and a muting configurationindicating REs in which the base stations involved in the CoMP operationlimit transmission.
 27. The apparatus of claim 26, further comprising:means for detecting, by the apparatus, that at least one of CSI-RS andmuting is dropped on certain subframes; and wherein the means fordetermining determine that one or more data REs previously allocated forat least one of CSI-RS or muting become available for data transmissionon those certain subframes.
 28. The apparatus of claim 17, furthercomprising means for receiving, by the apparatus, signaling thatprovides an indication of a type of CoMP scheme used for the CoMPoperation, wherein the signaling that provides the indication of thetype of CoMP scheme used for the CoMP operation and the particular basestations is provided via a semi-static configuration.
 29. The apparatusof claim 17, further comprising means for receiving, by the apparatus,signaling that provides an indication of a type of CoMP scheme used forthe CoMP operation, wherein the signaling that provides the indicationof the type of CoMP scheme used for the CoMP operation and theparticular base stations is provided via a dynamic indication conveyedusing a physical downlink control channel (PDCCH).
 30. The apparatus ofclaim 17, wherein the base stations involved in the CoMP operationcomprise base stations of different power classes in a heterogeneousnetwork.
 31. The apparatus of claim 17, wherein the data is receivedfrom each of the base stations involved in the CoMP operation.
 32. Theapparatus of claim 17, wherein the data is received from a subset of thebase stations involved in the CoMP operation.
 33. An apparatus forwireless communications, comprising: a processing system configured to:determine, by the apparatus, a set of data resource elements (REs) usedfor a Coordinated Multipoint (CoMP) operation, wherein the determinationis based on data REs available to the CoMP operation and signaling thatprovides a starting symbol index of data REs; and process, by theapparatus, data received via the CoMP operation on the determined set ofdata REs, wherein processing the data received via the CoMP operationcomprises processing common modulation symbols transmitted by each of aplurality of base stations involved in the CoMP operation on a subset ofthe determined set of data REs.
 34. A non-transitory computer-readablemedium for wireless communications, the non-transitory computer-readablemedium comprising code for: determining, by a user equipment (UE), a setof data resource elements (REs) used for a Coordinated Multipoint (CoMP)operation, wherein the determination is based on data REs available tothe CoMP operation and signaling that provides a starting symbol indexof data REs; and processing, by the UE, data received via the CoMPoperation on the determined set of data REs, wherein processing the datareceived via the CoMP operation comprises processing common modulationsymbols transmitted by each of a plurality of base stations involved inthe CoMP operation on a subset of the determined set of data REs.